Intake manifolds formed by injection molding of polymers are well known in the engine arts. A manifold assembly typically comprises an upper manifold, containing the air entry and control apparatus and an air plenum, and a lower manifold, containing individual runners for supplying air distributed from the upper manifold to the individual intake valve ports in the engine head. The upper and lower manifolds typically are formed separately and are joined as by vibration welding prior to being assembled to an engine. A lower manifold typically is further manufactured by injection molding of a top shell and a bottom shell which are subsequently joined as by vibration welding.
In forming a lower manifold for a V-style engine, a serious manufacturing problem is encountered, which problem is solved by the present invention. In the prior art, the bottom shell is formed as a single unit having a die draft direction that must be along the vertical axis of the shell in order for the mold to exit both left and right banks of the runners. Such a lower manifold is said to be of “two-piece” construction (upper and lower shells). The required die draft direction and split core mold construction restricts the individual runners to substantially rectangular cross-sections which shape is sub-optimal for air delivery and fuel/air mixing.
Further, in order to avoid the use of auxiliary molding slides, which can result in significant increases in cost, molding cycle time, and risk in a productive environment, the seal groove in the manifold face that mates with an engine head must be formed with divergent walls to permit removal of the part from the mold. This groove geometry is not optimal because a ring seal is not reliably retained in the groove during engine assembly without resort to adhesives or mechanical retention devices. Optimally, the groove walls are parallel to each other and perpendicular to the mating faces of the manifold and the engine head to spontaneously retain a seal ring during engine assembly, but such grooves cannot be formed by die drafting along the shell axis without use of an auxiliary molding slide.
What is needed in the art is a method and apparatus of forming a lower shell for a V-style intake manifold wherein the seal groove walls are parallel to each other and perpendicular to the mating faces of the manifold and the engine head without use of an auxiliary molding slide.
It is a principal object of the present invention to provide a lower shell for a V-style intake manifold wherein the seal groove walls are parallel to each other and perpendicular to the mating faces of the manifold and the engine head.